Microplastic-Derived Carbon Emissions: From Granular Carbon to Dissolved Organic Carbon and Carbon Dioxide under Ultraviolet Radiation

As a hydrocarbon polymer, microplastics (MPs) consisted of abundant carbon. Previous studies mostly focused on the surface degradation of MPs and the release of dissolved organic carbon (DOC) during aging processes, while the information about MP-derived carbon emission from granular carbon (GC) to DOC and carbon dioxide (CO₂) is limited. This study examined the dynamic changes in MP carbon from GC loss to the formation of DOC and CO₂ by selecting polystyrene (PS) and polybutylene succinate (PBS) as representative traditional and biodegradable MPs under ultraviolet (UV) radiation and mechanical abrasion. Results revealed that PS and PBS exhibited broken surfaces after UV radiation, and the mass and GC content of PS and PBS significantly decreased. The GC loss in PS and PBS was mainly converted into DOC, with only a small portion converted into CO₂. The GC loss and DOC increase in PBS exceeded those in PS, while PBS exhibited lower CO₂ content than PS. OH^• and O₂^•- were identified as the key factors influencing the UV-induced degradation of PS and PBS. This study provides new insights into the carbon emissions of MPs throughout their environmental degradation lifecycle and their contribution to global carbon emissions.